ISSN:
1432-136X
Keywords:
Hemoglobin
;
Three-state MWC model
;
Oxygenation
;
Organic phosphate
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary Oxygen equilibria in tench hemoglobin were analysed according to a three-state MWC model. In addition to theT andR states of the traditionally used two-state model, the three-state model introduces an additional state, theS state, when organic phosphates bind to theT-structure hemoglobin. Under conditions covering natural red cell pH values and nucleoside triphosphate-hemoglobin ratios, it was possible to closely fit experimental data to the three-state equation with constant values of the association constantsK R ,K T , andK S , and with only the allosteric constantsL andM varying with effector conditions. Thus, in contrast to a twostate analysis of oxygen equilibria, the three-state analysis was consistent with the basic assumption of the MWC model, that heterotropic ligands only affect allosteric constants and not association constants. The temperature-dependence of the three-state parameter values showed that in the presence of nucleoside triphosphate the dominance of theS state over theT state was most pronounced at low temperatures. Furthermore, the numerical values of the enthalpy and entropy change of oxygenation were lower in theS state than in theT andR states, and the enthalpy and entropy change for the allostericS→R transition were much larger than for theT→R transition.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01075672
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